1. Field of the Invention
The present disclosure generally relates to a frame of an image forming apparatus such as a copier, a printer, a facsimile machine, or the like, and an image forming apparatus using the frame.
2. Description of the Background Art
Typically, image forming apparatuses employ a frame to define the apparatus, allow access to the interior of the apparatus, and support functional units inside the apparatus at precise positions within the apparatus, wherein the functional units may include an image forming unit but not limited to thereto. The frame supports the functional units either by direct contact or indirectly.
Ideally, the image forming apparatus is installed on a flat or level surface to reduce strain on or distortion of the frame of the apparatus. However, for various reasons, some image forming apparatuses may be installed on a surface that is not flat or level, which may strain or distort the frame of the apparatus. Such strain on or distortion of the frame may cause strain on or distortion of the image forming unit supported by the frame, which in turn may result in image quality deterioration. For example, the image quality deterioration may be appears as: two parallel lines in an image may be undesirably produced as unparallel lines; a straight line in an image may be undesirably produced as curved line; a right angle in an image may be undesirably deviated from the right angle; and two color images may not be superimposed one on another correctly.
Placing the image forming apparatus on a surface that is not level affects not only the quality of imaging. For example, typically, for ease of operation and servicing, image forming apparatuses are physically accessible both externally and internally from a front side of the apparatus, so that an operation panel can be operated, or replaceable units can be easily installed in and removed from the apparatus. Accordingly, some units that are not inspected or checked on a daily basis may be disposed at a rear side of apparatus. For example, a driving unit, a power unit or the like may be disposed at the rear side of apparatus, and thus not easily accessible by a user.
A further complication is that, to reduce a footprint of the image forming apparatus, such units disposed at the rear side of apparatus may be projected rearward outside of the footprint of apparatus. Consequently, some image forming apparatuses may have a center of gravity at a rearward of the apparatus relative to a physical center of the apparatus.
When an image forming apparatus having a center of gravity at its rearward portion is installed on an uneven surface, the image forming apparatus may be unstable. For example, the rear side of apparatus may land firmly on the floor but the front side of apparatus may not land firmly on the floor; one of a right and left side of front portion of apparatus may not land firmly on the floor; and a frame in the front side of apparatus may more likely deform. Consequently, strain or distortion may be more likely to occur at the front side of the frame of image forming apparatus. To reduce such strain or distortion, stiffness of frame may need to be enhanced at the front side of the image forming apparatus so as to attain good level of shape retentiveness of the frame.
JP-3439301-B discloses an image forming apparatus having an image forming unit, a sheet feed unit disposed under the image forming unit, a front plate, a rear plate, and a base plate. The front plate and rear plate are fixed on a front and a rear of the base plate. Accordingly, the image forming unit and the sheet feed unit may be disposed in a space defined by the front and rear plates. In such a frame, the front plate may not have a good level of stiffness because some open space is required for withdrawing a sheet cassette from the sheet feed unit. Such image forming apparatus may further include an image scanning unit over the image forming unit. Specifically, one or more support pillars may be fixed on top rim portions of the front plate and extended in an upward direction to support the image scanning unit. The support pillars can be used to reduce strain or distortion of the image scanning unit disposed over the image forming unit. But the support pillars may not be extended to the base plate or a portion supporting the sheet feed unit. Accordingly, such configuration may not effectively enhance stiffness of the frame at the front side. Consequently, strain on or distortion of the image forming unit may occur due to a lack of stiffness of the frame.
JP-H10-310267-A discloses an image forming apparatus including a frame, an image forming unit, and a sheet feed unit, in which the frame supports the image forming unit, and the sheet feed unit is disposed under the image forming unit. The frame may include a front plate and a rear plate, support pillars, and a base plate to which the support pillars are fixed. The image forming unit may be supported by one front plate and one rear plate, and the sheet feed unit may be supported by another front plate and another rear plate. The front plate and the rear plate are supported by the support pillars fixed on the base plate. Each of the support pillars may have a hollow structure, which means the support pillar may have a hollow cross-section.
In such frame, the support pillars, which support the front and rear plates, are fixed on the base plate, by which stiffness of the frame may be enhanced. Further, because one set of front and rear plates are provided for the image forming unit and another set of front and rear plates are provided for the sheet feed unit, strain on or distortion of the sheet feed unit may not cause strain on or distortion of the image forming unit.
In JP-3439301-B, the frame may not have the requisite shape retentiveness. Further, the front plate, supporting the image forming unit disposed over the sheet feed unit, is extended and fixed on the base plate, which is placed under the sheet feed unit. Accordingly, a size of front plate becomes greater relative to a size of the image forming unit. A greater front plate may have a lower precision on its physical dimensions, and may increase manufacturing cost, die or molding cost, and delivery cost, by which cost reduction may be hard to attain.
In JP-H10-310267-A, the frame may have a good level of shape retentiveness. However, the front plate is supported and positioned at a given plane of the support pillars, having the hollow square shape, parallel to the front plate. Such configuration may not position the front plate at a given position precisely. Further, hollow supports need a welding process for closing a gap of support pillar. Further, the support pillar may need a welding process and a joint member for fixing the support pillars, by which a manufacturing cost may increase compared to a support pillar having a U-shaped form. Further, such frame may need a plurality of front and rear plates, by which cost reduction may be hard to attain.